Speaker
Description
The James Webb Space Telescope (JWST) has opened a new frontier in strong gravitational lensing by providing the resolution and depth necessary to identify some of the most distant lenses ever discovered. Among these are group-scale lenses, systems of approximately 2–10 galaxies that bridge the gap between galaxy- and cluster-scale lenses. These systems offer magnifications up to ten times higher than galaxy-scale lenses ($\mu\sim 50$) whilst maintaining sufficiently simple mass models that allow for the ability to reconstruct the unlensed source morphology. We modelled a sample of five JWST group-scale lenses identified in the COSMOS-Web survey, leveraging JWST’s multi-band imaging to perform high-precision lens modelling. Our lens model accounts for the contribution of the 4-10 galaxies per system, whose contribution to the lens is key to reconstructing the source’s detailed morphology on an adaptive Voronoi mesh. Notably, we identified a spectroscopically confirmed source at $z=4.99$, which is HST-dark, allowing us to reconstruct its structure which provides an unprecedented view of this galaxy class emerging as key to high redshift galaxy evolution. The sample also includes two double-source plane lens candidates, one of which features the $z=4.99$ source. These systems therefore motivate an exploration of how JWST group-scale lenses can inform cosmological parameter inference, given they could extend the angular diameter distance redshift range–critical to cosmology–over a much more significant range than achievable with galaxy-scale lenses.
